Methods and apparatus to determine a state of a media presentation device

ABSTRACT

Methods and apparatus to determine a state of a media presentation device are disclosed. Example disclosed methods include generating a first set of weighted coefficients based on first audio received by first and second microphones at a first time. Example disclosed methods include generating a second set of weighted coefficients based on second audio received by the first and second microphones at a second time after the first time. Example disclosed methods include comparing the first set of coefficients and the second set of coefficients to generate a similarity value. Example disclosed methods include, when the similarity value satisfies a threshold, determining that the media presentation device is in a first state. Example disclosed methods include, when the similarity value does not satisfy the threshold, determining that the media presentation device is in a second state.

RELATED APPLICATION

This patent claims the benefit of U.S. Non Provisional application Ser. No. 15/925,360, (Attorney Docket No. 20004/109485US03), entitled “Methods and Apparatus to Determine a State of a Media Presentation Device,” which was filed on Mar. 19, 2018, which claims priority to U.S. Non-Provisional application Ser. No. 14/926,885 (Attorney Docket No. 20004/109485US02), entitled “Methods and Apparatus to Determine a State of a Media Presentation Device,” which was filed on Oct. 29, 2015, which claims the benefit of U.S. Provisional Application Ser. No. 62/142,771 (Attorney Docket No. 20004/109485US01), entitled “Methods and Apparatus to Determine a State of a Media Presentation Device,” which was filed on Apr. 3, 2015. These applications are hereby incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

This disclosure relates generally to market research, and, more particularly, to methods and apparatus to determine a state of a media presentation device.

BACKGROUND

Audience measurement systems may be used to identify content output by a media presentation device. For example, a metering device can be equipped with microphone(s) to identify program content emanating from a media presentation device, such as a television (TV). An audio signal captured by the microphone(s) is processed either to extract an embedded watermark from the audio signal or convert the audio signal to a signature for matching against signatures stored in a reference database. Audio watermarks are embedded in media program content prior to distribution of the media program content for consumption. Reference audio signature databases are created from broadcast or distributed media program content.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example system including a meter to determine a state of a media presentation device.

FIG. 2 shows an example implementation of a metering device such as the meter of FIG. 1.

FIG. 3 illustrates an example implementation of a source detector such as the source detector of FIG. 2.

FIG. 4 depicts an example filter weight distribution corresponding to filter weights that indicate a monitored media presentation device is turned on.

FIG. 5 depicts another example filter weight distribution corresponding to filter weights that indicate a monitored media presentation device is turned off

FIG. 6 depicts an example filter apparatus implementing an adaptive least mean square algorithm using a finite impulse response (FIR) filter, such as in the example source detector of FIG. 3.

FIG. 7 depicts an example implementation of a state determiner such as the state determiner of FIG. 3.

FIG. 8 is a flow diagram representative of example machine readable instructions that may be executed to implement a monitoring and audience measurement process including an example metering device and its source detector of FIGS. 1-3 and 6-7.

FIG. 9 is a flow diagram providing additional detail representative of example machine readable instructions that may be executed to implement a portion of the flow diagram of FIG. 8.

FIG. 10 is a flow diagram providing additional detail representative of example machine readable instructions that may be executed to implement a portion of the flow diagram of FIG. 8.

FIG. 11 is a block diagram of an example processor system structured to execute the example machine readable instructions represented by FIGS. 8-10 to implement the example metering device and its source detector of FIGS. 1-3 and 6-7.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific examples that may be practiced. These examples are described in sufficient detail to enable one skilled in the art to practice the subject matter, and it is to be understood that other examples may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the subject matter of this disclosure. The following detailed description is, therefore, provided to describe example implementations and not to be taken as limiting on the scope of the subject matter described in this disclosure. Certain features from different aspects of the following description may be combined to form yet new aspects of the subject matter discussed below.

When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

In many microphone-based audience measurement environments, it is necessary to determine a source of audio signals being captured by a metering, monitoring, or measurement device (referred to herein as a “metering device or a meter” for illustrative brevity). If a source of captured audio signal is not properly identified, error is introduced into the audience measurement data that is generated based on the captured audio.

However, in some environments, a monitoring or metering device captures audio not only emanating from a media presentation device of interest, but also from other sources including ambient noise, speech signals from viewers talking to each other, etc. As disclosed herein, a source of the captured audio is identified to avoid erroneous audience measurement stemming from audio that is not emanating from the media presentation device of interest.

Examples disclosed herein facilitate audience measurement to determine whether audio being captured is emanating from the media presentation device of interest. When watermarks embedded in media are not successfully extracted, signatures computed from the microphone-captured audio may or may not represent the audio emanating from the media presentation device of interest. For example, the media presentation device of interest may be turned down or off, and the source of audio captured by the microphone can be any one of a plurality of other possible sources (e.g., people talking, other equipment in the room, ambient noise, etc.). In some such cases, it is possible to obtain false matches for program signature information when monitoring signatures generated by a metering or monitoring device are compared against a large number of reference signatures in a reference database. Certain examples confirm the media presentation device as source by analyzing the audio signals captured by the metering device.

Examples disclosed herein facilitate reducing instances of false matching by distinguishing audio emanating from the media presentation device of interest from audio generated by other potential sources. For example, disclosed examples facilitate identifying the media presentation device of interest as the source of the detected audio by analyzing the audio captured by the metering device to determine whether the media presentation device of interest is 1) turned on or 2) turned down or off

Certain examples determine whether the media presentation device of interest is 1) turned on or 2) turned down or off by determining whether or not the detected audio matches a characteristic of audio previously detected from the media presentation device. If the detected audio matches a characteristic of audio previously detected from the media presentation device, then the media presentation device is inferred to be turned on. However, if the detected audio does not match a characteristic of audio previously detected from the media presentation device, then the media presentation device is inferred to be turned down or turned off.

When metering devices incorrectly credit exposure minutes, one or more household tuning estimates and/or projections may be over-reported and/or otherwise inflated. Additionally, attempted detection of watermarks and/or other codes by metering devices can return false positives and/or erroneous data if ambient noise interferes with proper capture and analysis of audio information from a media presentation device of interest. Example methods, apparatus, systems and/or articles of manufacture disclosed herein distinguish instances of ambient sound to be ignored from instances of audio from a media presentation device of interest that are to be monitored.

Examples disclosed herein provide methods of determining a state of a media presentation device. Disclosed example methods include generating a first set of weighted coefficients based on first audio received by first and second microphones at a first time. Disclosed example methods include generating a second set of weighted coefficients based on second audio received by the first and second microphones at a second time after the first time. Disclosed example methods include comparing the first set of coefficients and the second set of coefficients to generate a similarity value. Disclosed example methods include, when the similarity value satisfies a first threshold, determining that the media presentation device is in a first state. Disclosed example methods include, when the similarity value does not satisfy the first threshold, determining that the media presentation device is in a second state. Disclosed example methods include controlling a metering device based on the state of the media presentation device.

Examples disclosed herein provide tangible computer readable storage media having instruction that, when executed, cause a machine to generate a first set of weighted coefficients based on first audio received by first and second microphones at a first time. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to generate a second set of weighted coefficients based on second audio received by the first and second microphones at a second time after the first time. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to compare the first set of coefficients and the second set of coefficients to generate a similarity value. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to, when the similarity value satisfies a first threshold, determine that the media presentation device is in a first state. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to, when the similarity value does not satisfy the first threshold, determine that the media presentation device is in a second state. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to control a metering device based on the state of the media presentation device.

Examples disclosed herein provide apparatus including a metering device including a programmed processor. Disclosed example apparatus include the processor programmed to generate a first set of weighted coefficients based on first audio received by first and second microphones at a first time. Disclosed example apparatus include the processor programmed to generate a second set of weighted coefficients based on second audio received by the first and second microphones at a second time after the first time. Disclosed example apparatus include the processor programmed to compare the first set of coefficients and the second set of coefficients to generate a similarity value. Disclosed example apparatus include the processor programmed to, when the similarity value satisfies a first threshold, determine that the media presentation device is in a first state. Disclosed example apparatus include the processor programmed to, when the similarity value does not satisfy the first threshold, determine that the media presentation device is in a second state. Disclosed example apparatus include the processor programmed to control a metering device based on the state of the media presentation device.

Examples disclosed herein provide methods of determining a state of a media presentation device. Disclosed example methods include generating a first set of weighted coefficients based on first audio received by first and second microphones at a first time. Disclosed example methods include generating a second set of weighted coefficients based on second audio received by the first and second microphones at a second time after the first time. Disclosed example methods include calculating a dot product between the first set of coefficients and the second set of coefficients. Disclosed example methods include, when the calculated dot product satisfies a threshold, determining that the media presentation device is in a first state (e.g., turned on or activated, etc.). Disclosed example methods include, when the calculated dot product does not satisfy the threshold, determining that the media presentation device is in a second state (e.g., turned off or powered down, etc.).

Examples disclosed herein provide tangible computer readable storage media having instruction that, when executed, cause a machine to generate a first set of weighted coefficients based on first audio received by first and second microphones at a first time. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to generate a second set of weighted coefficients based on second audio received by the first and second microphones at a second time after the first time. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to calculate a dot product between the first set of coefficients and the second set of coefficients. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to, when the calculated dot product satisfies a threshold, determine that the media presentation device is in a first state. Disclosed example computer readable storage media have instructions that, when executed, further cause the machine to, when the calculated dot product does not satisfy the threshold, determine that the media presentation device is in a second state.

Examples disclosed herein provide apparatus including a metering device. Disclosed example metering devices are to generate a first set of weighted coefficients based on first audio received by first and second microphones at a first time. Disclosed example metering devices are to generate a second set of weighted coefficients based on second audio received by the first and second microphones at a second time after the first time. Disclosed example metering devices are to calculate a dot product between the first set of coefficients and the second set of coefficients. Disclosed example metering devices are to, when the calculated dot product satisfies a threshold, determine that the media presentation device is in a first state. Disclosed example metering devices are to, when the calculated dot product does not satisfy the threshold, determine that the media presentation device is in a second state.

Examples disclosed herein provide methods of determining a source location for an audio signal. Disclosed example methods include processing a captured audio signal to generate a first set of weighted coefficients characterizing the captured audio signal. Disclosed example methods include comparing the first set of weighted coefficients to a second set of weighted coefficients representing a reference audio signal originating from a first location to generate a similarity value. Disclosed example methods include, when the similarity value satisfies a comparison threshold, identifying a source location of the captured audio signal as the first location. Disclosed example methods include, when the similarity value does not satisfy the comparison threshold, identifying the source location of the captured audio signal as a second location.

Examples disclosed herein provide a metering device including a processor particularly programmed to at least determine a source location for an audio signal by processing a captured audio signal to generate a first set of weighted coefficients characterizing the captured audio signal. The processor of the disclosed example metering device is programmed to at least determine a source location for an audio signal by comparing the first set of weighted coefficients to a second set of weighted coefficients representing a reference audio signal originating from a first location to generate a similarity value. The processor of the disclosed example metering device is programmed to at least determine a source location for an audio signal by, when the similarity value satisfies a comparison threshold, identifying a source location of the captured audio signal as the first location. The processor of the disclosed example metering device is programmed to at least determine a source location for an audio signal by, when the similarity value does not satisfy the comparison threshold, identifying the source location of the captured audio signal as a second location.

Examples disclosed herein include example systems and methods for determining whether or not the audio captured by a monitoring device is from a media presentation device of interest when measuring audience member exposure to media. In the examples disclosed herein, two microphones are separated by a fixed distance to monitor the audio present in a room. Audio emanating from different locations within the room create audio signals detected by the microphones that are time delayed with respect to each other and have different multi-path interference effects that are controlled by room acoustics as well as audio source location. In the examples disclosed herein, the differences between the audio signals are analyzed by an adaptive equalization algorithm using a finite impulse response (FIR) filter. The example filter taps or coefficients generated by applying the FIR filter constitute a feature vector (e.g., a set of coefficients) that characterizes the audio source (e.g., an identity and/or location of the audio source, etc.). In the examples disclosed herein, the set of coefficients obtained while the media presentation device is ON is used as a vector to uniquely identify future audio signals from the media presentation device as well as to reject audio signals from other sources. An example baseline (e.g., reference) vector is generated during an interval in which the audio from the media presentation device is confirmed by the successful extraction of watermarks embedded in the media presented by the media presentation device, for example.

Example Monitoring and Determination Systems

FIG. 1 depicts an example system 100, depicted in an example room 110 having a media presentation device 120 (e.g., a television, other display or monitor, etc.) including speakers 122, 124 providing audio 126 in the room 110. While the example of FIG. 1 depicts a typical room 110 in a household, the room 110 can be any space, public or private, including a home, restaurant, bar, vehicle, bus, boat, etc. The example system 100 includes an example metering device 130 including a pair of microphones 132 and 134, a source detector 136, a decoder 138, and a creditor 139.

The example source detector 136 of the metering device 130 determines a state of the example media presentation device 120. The metering device 130 of the illustrated example is disposed on or near the media presentation device 120 and may be adapted to perform one or more of a plurality of metering methods (e.g., channel detection, watermark detection, collecting signatures and/or codes, etc.) to collect data concerning the media exposure of the metering device 130, and thus, the media exposure of one or more audience member(s) 140, 142 with respect to the media presentation device 120.

Depending on the type(s) of metering that the metering device 130 is adapted to perform, the metering device 130 may be physically coupled to the media presentation device 120 or may instead be configured to capture signals emitted externally by the media presentation device 120 such that direct physical coupling to the media presentation device 120 is not required. For instance, in this example, the metering device 130 is not physically or electronically coupled to the monitored media presentation device 120. Instead, the metering device 130 is provided with at least one audio sensor, such as, for example, a microphone, to capture audio data regarding in-home media exposure for the audience member(s) 140, 142. Similarly, the example metering device 130 is configured to perform one or more of a plurality of metering methods (e.g., collecting watermarks, signatures and/or codes, etc.) on the collected audio to enable identification of the media to which the audience members 140, 142.

As shown in more detail in the example of FIG. 2, the metering device 130 is provided with two example microphones 132 and 134, separated by a distance D_(m), to record an audio signal 126 from the media presentation device 120. The example media presentation device 120 (e.g., a television set) has two speakers 122 and 124. Both speakers 122 and 124 reproduce or emit the audio signal 126 that is sensed by the microphones 132 and 134. In a typical room 110, multiple reflections may occur and the resulting audio signal 126 sensed by microphones 132 and 134 represents the combined effect of a direct wave and these reflections. Similarly, audience members 140, 142 talking to each in the room 110 other can create audio signals 144, 146 that are sensed by the microphones 132 and 134, as direct waves and/or as reflections.

In order to identify a single audio signal for metering, the example source detector 136 uses an algorithm, such as an adaptive least mean square algorithm, to construct a finite impulse response (FIR) filter that attempts to convert the audio (e.g., the audio signal 126, 144, and/or 146) captured by the first microphone 132 to a new synthetic signal (also referred to herein as a filtered audio signal) that is as close as possible, in a least mean squared sense, to the audio captured by the second microphone 134. Coefficients or “filter taps” of the corresponding adaptive filter depend on, for example, a location of the audio/media source (e.g., the media presentation device 120, the audience members 140, 142, etc.) of audio (e.g., the audio signal 126, 144, and/or 146, etc.) within the room 110 (e.g., assuming there is a single source). For example, a media presentation device 120 (e.g., a television set, etc.) equipped with two or more speakers (e.g., the speakers 122, 124, etc.) is considered to be a single source such that substantially the same audio waveform emanates from the speakers 122, 124 connected to the media presentation device 120). Coefficients or “filter taps” of the corresponding adaptive filter also depend on, for example, a separation between the microphones (D_(m)). Coefficients or “filter taps” of the corresponding adaptive filter also depend on, for example, acoustic characteristics of the room 110 determined by walls and/or other objects in the room 110 (e.g., devices, furniture, etc.). The source detector 136 assumes microphone separation and acoustic characteristics are constant for the coefficients that characterize the audio source.

As described further below, an adaptive algorithm subtracts the filtered version of the audio signal 126 received by the microphone 132 from the audio signal 126 received by the microphone 134. An adaptive filter generates the filter taps or coefficients used in the adaptive algorithm to yield information about similarity (or lack thereof) between the audio signals received by the microphones 132, 134, wherein the signal from the microphone 132 is delayed and filtered and the signal from the microphone 134 is not. Once the audio has been processed, the audio (e.g., audio signal 126, 144, 146, etc.) can be analyzed to determine a likely source of that audio and its associated status.

The example metering device 130 includes a decoder 138 and a creditor 139 in addition to the source detector 136 and microphones 132, 134. The decoder 138 receives and decodes audio received by the microphones 132 and 134 to extract a watermark and/or other code from the received audio. The decoder 138 works with the source detector 136 to determine whether or not the received audio is associated with the media presentation device 120 or from other ambient sound sources, such as audience members 140, 142, audio from another device, etc. If the decoder 138 identifies a valid watermark, for example, then the creditor 139 captures an identification of the media exposure and/or other audience measurement data based on the decoded watermark, code, etc. In some examples, the watermark is associated with a score (e.g., a reliability score) indicating a strength of or confidence in the decoded watermark. In some examples, a volume analysis is done in conjunction with the watermark identification to confirm that the watermark has been generated by a nearby monitored source instead of from a source that is farther away (e.g., spillover). In some examples, a signature and/or other code can be computed from the audio instead of or in addition to the watermark (e.g., when a watermark is not identified in the audio, etc.). The creditor 139 may also assign a location identifier, timestamp, etc., to the decoded data.

In certain examples, a home processing system (not shown) may be in communication with the meter 130 to collect media/audience exposure data (e.g., watermark, signature, location, timestamp, etc.) from the metering device 130 for further analysis, relay, storage, etc. As shown in the example of FIG. 1, data gathered by the meter 130 (e.g., watermark, signature, location, timestamp, etc.) can be relayed (e.g., directly or via the home processing system, etc.) via a network 150 to an audience measurement entity (AME) 160, such as a data collection facility of a metering entity (e.g., The Nielsen Company (US), LLC) for further tracking, analysis, storage, reporting, etc. Data can be relayed to the AME 160 via the network 150 (e.g., the Internet, a local area network, a wide area network, a cellular network, etc.) via wired and/or wireless connections (e.g., a cable/DSL/satellite modem, a cell tower, etc.).

In the illustrated example of FIG. 1, the AME 160 includes a monitoring database 162 in which to store the information from the monitored room 110 and a server 164 to analyze data aggregated in the monitoring database 162. The example AME 160 may process and/or store data received from other metering device(s) (not shown) in addition to the metering device 130 such that a plurality of audience members can be monitored and evaluated. In another example, multiple servers and/or databases may be employed as desired.

For example, the example server 164 collects the media exposure data from the meter 130 and stores the collected media exposure data in the example monitoring database 162. The example server 164 processes the collected media exposure data by comparing the codes, metadata, and/or signatures in the collected media exposure data to reference codes and/or signatures in a reference database to identify the media and/or station(s) that transmit the media. Examples to process the codes and/or signatures in the collected media exposure data are described in U.S. patent application Ser. No. 14/473,670, filed on Aug. 29, 2014, which is hereby incorporated herein by reference in its entirety. The example server 164 awards media exposure credits to media identified in the collected media exposure data, for example. In some examples, the media exposure credits are associated with demographic information corresponding to the audience member 140, 142 and/or type of audience member 140, 142 associated with the meter 130 that collected the media exposure data.

FIG. 3 illustrates an example implementation of the example source detector 136 of FIG. 2. In the illustrated example of FIG. 3, the example source detector 136 includes an adaptive audio filter 302, a weight adjuster 304, an audio comparator 306, and a state determiner 308. The example adaptive audio filter 302 samples audio received by the first microphone 132 at a specified sampling rate. In some examples, the adaptive audio filter 302 uses a 48 kHz sampling rate and uses 512 filter taps or weights (e.g., with values starting at zero and increasing based on signal delay). In such examples, the 512 filter taps or weights correspond to a maximum time delay of 10.66 milliseconds ( 1/48000 second per sample×512 samples). Because the microphones 132, 134 are close to one another (e.g., distance D_(m)) relative to a distance between the meter 130 and the potential audio sources 120, 140, 142, a delay of the audio signal 126 is below a maximum time delay value (e.g., 10.66 milliseconds). In some examples, other sampling rates, such as 24 kHz, may be used. In such examples, the filter weights used by the adaptive audio filter 302 become relatively constant values in, for example, less than a second from the start of the detected audio processing.

The set of weights (e.g., {W_(m), m=0,1, . . . M−1}, also referred to as a feature vector) generated by the weight adjuster 304 characterizes a particular source of audio. In some examples, filter weights are modified and/or generated by the weight adjuster 304 based on feedback from the audio comparator 306 and/or other external input regarding the audio signal 126.

The audio comparator 306 analyzes the filtered audio signal provided by the adaptive audio filter 302 from the microphone 132 and compares it to the unfiltered audio signal input from the microphone 134. An error signal, used to impact the set of filter coefficients, can be also generated by the audio comparator 306 based on the comparison. If the audio comparator 306 matches the filtered and unfiltered signals and determines that the filtered audio detected by the first microphone 132 is substantially the same as the unfiltered audio detected by the second microphone 134, the error signal decreases to a low value. If, however, the filtered audio from the first microphone 132 is distinct from the unfiltered audio from the second microphone 134, the error signal increases in value. An increase in the error signal can trigger a re-calculation of the filter weight coefficients by the adaptive audio filter 302 to help ensure that the filtered audio from the microphone 132 matches the unfiltered audio from the microphone 134 and properly characterizes the audio source. The coefficients characterizing that audio source can then be compared to a reference to determine whether the audio source is the media presentation device 120 or is some other source of audio (e.g., people 140, 142 talking, ambient noise, another device emitting sound in the same room and/or another room, etc.).

In the illustrated example of FIG. 3, the adaptive audio filter 302 and/or the audio comparator 306 examines the filter coefficient distribution to help ensure that the filter taps or weights generated by the weight adjuster 304 have a decay characteristic (e.g., in which coefficient weights “decay” or reduce to zero over time). In the illustrated example, audio received by the second microphone 134 is delayed relative to the audio received by the first microphone 132 when the media presentation device 120 is the source of audio (e.g., the audio 126 of FIG. 1) because the first microphone 132 is relatively closer (in the example of FIG. 1) to the media presentation device 120 than the second microphone 134. Phrased differently, a relative delay between audio detected by the first and second microphones 132, 134 is dependent on the location of the meter 130 relative to the media presentation device 120. In some examples, the relative delay is based is also based on multiple sound wave paths in a room (e.g., the room 110 of FIG. 1) due to walls and other objects that contribute to acoustic reflections.

The example weight adjuster 304 generates and/or updates a set of filter coefficients having a magnitude that exponentially decreases as the index increases (e.g., a decay characteristic). An example filter weight distribution corresponding to filter weights that indicate that measured audio matches characteristics of audio emitted by the monitored presentation device 120, and, therefore, indicate that the monitored media presentation device 120 is turned on is shown in FIG. 4.

As shown in the example of FIG. 4, an example filter weight distribution 402 includes a plot of a plurality of filter weight coefficients 404 along an index 406, such as time (e.g., milliseconds), sample, etc. Individual weights 408-413 along the distribution form the set of filter coefficients used as a feature vector to represent the audio and calculate similarity between the audio signal and a reference vector.

The example audio comparator 306 of FIG. 3 calculates a signal error between the audio signal received by the first microphone 132 and then filtered and the audio signal received by the second microphone 134. As described above, if the audio comparator 306 matches the filtered and unfiltered signals and determines that the filtered audio detected by the first microphone 132 is substantially the same as to the unfiltered audio detected by the second microphone 134, the error signal has a low value (e.g., close to zero), and the associated weight coefficients can be used for analysis. If, however, the filtered audio from the first microphone 132 is distinct from the unfiltered audio from the second microphone 134, the error signal has a high value (e.g., one), and associated weight coefficients may be unsuitable for analysis. The example weight adjuster 304 adjusts and/or recalculates the weighted coefficients generated by the adaptive audio filter 302 based on the error signal till the filtered and unfiltered signals match and can then be compared to a reference to determine whether the monitored presentation device 120 is the source of the detected audio (and is therefore inferred to be “on” or “off”, for example).

For example, filter weight coefficients are determined by an echo cancellation algorithm, described further below with respect to FIG. 6, so that, if the microphone 132 output is filtered using these coefficients and added to the microphone 134 signal, the net result is a very low energy audio output. Under ideal conditions, signals from 132 (filtered) and 134 (unfiltered) should perfectly cancel one another. In reality, however, the difference between filtered and unfiltered microphone inputs should be close to zero if the signals from 132 and 134 are both indicative of audio from the media presentation device 120.

In an example, suppose a difference in signals between microphone 132 and microphone 134 is a constant delay equivalent to ten samples. In this example, an FIR filter includes a single high value at a tenth coefficient and remaining filter coefficients are zero. However, room acoustics may complicate the filter coefficient analysis (e.g., remaining filter coefficients may be low but not exactly zero). Thus, in such an example, results include a primary audio “beam” with a delay of ten samples when measured at microphone 132 relative to microphone 134. The primary beam provides a high value coefficient at index 10 (e.g., corresponding to the delay of ten samples) followed by several smaller coefficients at indexes 11, 12, etc.

After the inputs from microphones 132 and 134 have been compared to reconcile the audio and generate the set of filter coefficients, the example audio comparator 306 provides the set of filter coefficients to the example state determiner 308. The state determiner 308 compares the set of filtered coefficients associated with the received audio signal 126 to a stored representation (e.g., a reference set of filter coefficients) of a reference signal indicating that the media presentation device 120 is turned on. If the received audio signal 126 matches or closely approximates characteristics of the reference signal (e.g., based on a comparison of the coefficient sets resulting in generation of a similarity value), then the state determiner 308 infers that the media presentation device 120 is turned on and outputting the audio 126. That is, characteristics of the audio signal 126, as identified by its set of filter coefficients, indicate a location of source for the audio signal 126 that matches a predetermined or “known” location of the media presentation device 120 as indicated by the reference set of filter coefficients.

Otherwise, the state determiner 308 infers that the media presentation device 120 is turned off or is otherwise not outputting detectable audio (e.g., is muted, the volume is turned down past a detectable threshold, etc.). Thus, a source of the audio detected by the microphones 132, 134 is other than the media presentation device 120. In some examples, as described further below, a mathematical operation such as a dot product determines a similarity of characteristics between the weight coefficients of the detected audio and reference coefficients. In some examples, reference coefficients can be recalculated by the weight adjuster 304 to accommodate a re-positioning of the media presentation device 120, an introduction of a new audio source in the room 110, etc. Recalculation or recalibration of reference coefficients can be based on one or more factors such as a time period without detecting audio having similar coefficients to the reference, identification of a valid watermark having a high reliability score, passage of a defined period of time (e.g., based on statistical analysis of prior media exposure data, household characteristic, etc.), etc.

When the meter 130 is extracting audio watermarks embedded in the detected audio, the state determiner 308 infers that the media presentation device 120 is likely the source (or a significant contributor) of the detected audio. As mentioned above, periodically and/or at certain defined times (e.g., as preset in the source detector 136, based on accuracy of watermark detection, based on quality of feedback, etc.), the example state determiner 308 stores filter coefficients generated by the example adaptive audio filter 302 and weight adjuster 304 during respective intervals as baseline (e.g., reference) filter coefficients {W_(m1), m=0,1, . . . M−1}.

In some examples, if the state determiner 308 determines that the baseline filter coefficients generated by the weight adjuster 304 do not exhibit a decay characteristic (e.g., decreasing as the index increases), the example adapter audio filter 302 and the example audio comparator 306 interchange the audio signals received by the first and second microphones 132 and 134 (e.g., so that now the signal received at the second microphone 134 is filtered and the signal received at the first microphone 132 remains unfiltered) and rerun the adaptation algorithm to obtain a more suitable set of baseline coefficients that exhibit a decay characteristic. The signals are interchanged to correct an assumption in relative position and delay between the media presentation device 120 and the microphones 132 and 134. For example, the filter coefficients generated by the weight adjuster 304 may not exhibit a decay characteristic when the signal from microphone 132 is processed relative to the signal from microphone 134 because the relative positions of the microphones 132, 134 with respect to the media presentation device 120 are such that audio received by the first microphone 132 is delayed relative to audio received by the second microphone 134 (rather than the initial assumption that audio received from microphone 134 is delayed with respect to audio received by microphone 132).

In some examples, when the media presentation device 120 is turned off, there may be other sources of audio in the room 110, such as audience members 140, 142 talking to each other. In such examples, the weight adjuster 304 generates a new or updated set of coefficients {W_(m2), m=0,1, . . . M−1} for the audio 144, 146. FIG. 5 shows filter coefficients generated by the weight adjuster 304 corresponding to filter weights that indicate that measured audio does not match characteristics of audio emitted by the monitored presentation device, and, therefore, the monitored media presentation device is turned down or off in such an example.

As shown in the example of FIG. 5, an example filter weight distribution 502 includes a plot of a plurality of filter weight coefficients 504 along an index 506, such as time (e.g., milliseconds), sample, etc. Individual weights 508-513 along the distribution form the set of filter coefficients used as a feature vector to represent the audio and calculate similarity between the audio signal and a reference vector.

Based on the filter weight coefficients from the weight adjuster 304 and signal comparison by the audio comparator 306, the state determiner 308 determines whether or not the monitored media presentation device 120 is 1) turned on or 2) turned off, down, or muted such that no audio signal 126 can be detected by the microphones 132, 134.

FIG. 6 shows an example filter apparatus 600 which can be included, for example, in the source detector 136 of the metering device 130 (e.g., illustrated in FIGS. 1-3) to help identify a source of audio detected by the microphones 132, 134 of the metering device 130. As shown in the example of FIG. 6, the example filter apparatus 600 can be used to implement all or part of the adaptive audio filter 302, weight adjuster 304, and audio comparator 306. The example filter apparatus 600 shown in FIG. 6 implements an adaptive echo cancellation algorithm and is configured to subtract a filtered version of detected audio recorded by the first microphone 132 from the detected audio recorded by the second microphone 134. In some examples, the microphones 132, 134 may also have picked up other ambient audio, including the human speech 144, 146.

As disclosed in more detail below, the adaptive filter 600 (e.g., an adaptive Finite Impulse Response (FIR) filter, etc.) generates filter coefficients or taps which, upon analysis, yield information about a similarity between the audio signals detected by the microphones 132, 134. Depending on a location of the source, the audio received by the microphone 134 may be delayed relative to the audio received by the microphone 132, or vice versa. In some examples, multiple sound wave paths exist due to reflections from walls and other objects in the room. Therefore, in order to subtract the effect of the audio detected by the first microphone 132 from the audio detected by second microphone 134, a FIR filter is used to delay and/or attenuate the audio detected by the first microphone 132, for example.

In the example illustrated in FIG. 6, audio samples 602 received by the microphone 132 are passed through a delay line 604, which includes a set of M shift registers D. In the illustrated example, X_(M−1), is a most recent sample, and X₀ is an oldest sample. An output Y₀ of the filter is shown in Equation 1 below:

$\begin{matrix} {Y_{o} = {\sum\limits_{m = 0}^{m = {M - 1}}{W_{m}{X_{m}.}}}} & {{Equation}\mspace{14mu} 1} \end{matrix}$

In Equation 1 above, {W_(m), m=0,1, . . . M−1} are weights whose initial values are set to 0. The set of weights may define a feature or reference vector. A current unfiltered input sample of audio 606 from the second microphone 134 is X_(d). In the illustrated example of FIG. 6, by summing 608 the weighted audio samples X_(M−1) to X₀ as shifted using shift registers D, the filter apparatus 600 operates to make the output Yo of the filter from the audio sample 602 of microphone 132 approximate the current input sample X_(d) from microphone 134 (e.g., Y₀≈X_(d)).

To verify the approximation, a difference 610 is obtained in comparing the filter output Y₀ to X_(d) to generate a difference signal X_(e) indicative of an error in the approximation. For example, if Y₀≈X_(d), then X_(e) should be at or near 0. However, if Y⁰≈X_(d), then X_(e) will be greater than 0. To help ensure that the approximation of Y₀ to X_(d) holds true, the weights W_(M−1), W_(M−2), W_(M), . . . , W₀ are adjusted 612 to new values based on an error signal X_(e) generated, for example, as shown in Equations 2 and 3 below:

X _(e)(n)=X _(d)(n)−Y ₀(n)  Equation 2;

W _(m)(n+1)=W _(m)(n)+μX _(e) X _(m)(n)  Equation 3.

In Equations 2 and 3 above, an index n is an iteration index denoting a time, indicated in sample counts, at which the modification in weights is made, and μ is a learning factor that is usually set to a low value (e.g., 0.05, etc.) in the illustrated example. This learning factor gradually minimizes a least mean squared (LMS) error in the output comparison as the filter output converges over the n iterations.

In certain examples, to determine a state (e.g., turned on or turned off) of the media presentation device 120, the example state determiner 308 calculates a dot product between a reference vector of filter coefficients and a comparison vector of filter coefficients {W_(m1), W_(m2)} and compares the result (e.g., referred to as a similarity value, comparison value, etc.) to a threshold (e.g., 0.5, etc.):

$\begin{matrix} {{A \cdot B} = {{\sum\limits_{m = 0}^{m = {M - 1}}{A_{m}B_{m}}} = {{A_{0}B_{0}} + {A_{1}B_{1}} + {\ldots \mspace{14mu} A_{M - 1}{B_{M - 1}.}}}}} & {{Equation}\mspace{14mu} 4} \end{matrix}$

The dot product (e.g., shown in Equation 4 between corresponding M coefficients of vectors A and B) or other similar mathematical comparison between a) a known reference set of coefficients indicative of audio characteristics from an audio source (e.g., the media presentation device 120) at a particular location in the room 110 and b) a second set of coefficients indicative of audio characteristics from a captured audio signal determines whether or not the captured audio originated from the same source as the reference audio (e.g., whether the audio signal 126 came from the media presentation device 120 or was instead generated by another source such as people 140, 142 in the room 110, etc.). If the analysis determines that the audio signal 126 originated from the media presentation device 120, then it can be inferred that the media presentation device 120 is turned on. Otherwise, it can be inferred that the media presentation device 120 is turned off or muted or turned down such that audio is not detectable from the media presentation device 120 by the microphones 132, 134. Audio that does not emanate from the media presentation device 120 is not metered, for example.

In the illustrated example, the threshold for dot product comparison may be specified (e.g., by a user, by a programmer, based on feedback from another application, etc.) to achieve a desired level of accuracy in identifying whether the media presentation device 120 is “ON” or “OFF”. If the result of the dot product satisfies (e.g., is greater than) the threshold, the example state determiner 308 determines that the media presentation device 120 is ON. For example, if the media presentation device 120 is ON, the result of the dot product may be close to 1.0 (e.g., assuming that the meter 130 has not been moved since the baseline coefficients were last calculated). If the result of the dot product does not satisfy (e.g., is less than) the threshold, the example state determiner 308 determines that the media presentation device 120 is OFF.

In certain examples, the dot product is calculated by converting each set of filter coefficients to a unit vector. Thus, the set of filter coefficients can be normalized for comparison between a comparison vector of measured filter coefficients and a reference vector of known filter coefficients. The unit vector or “normalized vector” represents a spatial direction in n-dimensional space. Then, the dot product is calculated using the unit vectors to determine an output in a range between negative one and positive one (−1.0 to +1.0). This output can be used to identify or otherwise characterize a source of the audio signal 126 and, extension, determine whether the monitored media presentation device 120 is outputting detectable audio (e.g., is turned on) or is not outputting detectable audio (e.g., is turned off or has its volume turned down or muted such that the media presentation device 120 is not outputting audio detectable by the meter 130).

The dot product or “scalar product” of two unit vectors in n-dimensional space is a scalar value calculated from a sum of the products of the corresponding n elements in each of the two unit vectors. If the two unit vectors are distinct unit vectors (e.g., orthogonal in n-dimensional space), then their dot product is zero. However, if the two unit vectors are identical, then their dot product is one. Therefore, two unit vectors that are different will have almost no dot product (e.g., close to 0), while two unit vectors that are the same or similar will have a dot product close to +1.0.

For example, suppose a reference vector obtained when the media presentation device 120 is confirmed “on”, such as the example set of filter coefficients from the example of FIG. 4, is represented as reference vector R={900, 100, −300, 0, 0, 0}. A first comparison filter coefficient vector C1={910, 120, −310, 0, 0, 0}. A second comparison filter coefficient vector, modeled after the example filter coefficients in the example of FIG. 5, C2={100, 0, 0, −200, 100, 200}.

In certain examples, coefficient vectors are normalized or converted to unit vectors as follows: u=v/|v|, where u represents the unit vector, v represents the original vector, and represents a magnitude of the vector v. For the first comparison vector C1, its unit vector can be determined as follows (values truncated for purposes of the illustrative example):

-   -   |C1|=√{square root over ((910)²+(120)²+(−310)²+0+0+0)}=968.81,         and     -   Unit vector CU1={910/968.81, 120/968.81, −310/968.81, 0, 0, 0}.         For the second comparison vector C2, its unit vector can be         determined as follows:     -   |C2|=√{square root over         ((100)²+0+0+(−200)²+(100)²+(200)²)}=316.23, and     -   Unit vector CU2={100/316.23, 0, 0, −200/316.23, 100/316.23,         200/316.23}.         For the reference vector R, its unit vector can be determined as         follows:     -   |R|=√{square root over ((900)²+(100)²+(−300)²+0+0+0)}=953.94,         and     -   Unit vector RU={900/953.94, 100/953.94, −300/953.94, 0, 0, 0}.

Using the above example values and Equation 4, a dot product of RU and CU1 can be computed as follows:

-   -   RU·CU1=(910/968.81*900/953.94)+(120/968.81*100/953.94)+(−310/968.81*−300/953.94)+0+0+0=0.999798.         Comparing the dot product result to the example threshold of 0.5         shows that the dot product of RU and CU1 is greater than the         threshold of 0.5 and close to 1.0. As described above, such a         result indicates that the audio signal 126 is emanating from the         media presentation device 120, and, therefore, the media         presentation device 120 is inferred to be turned on.

Similarly, a dot product of coefficient unit vector CU2 and reference unit vector RU can be determined as follows:

RU ⋅ CU 2 = (100/316.23 * 900/953.94) + (0 * 100/953.94) + (0 * −300/953.94) + (−200/316.23 * 0) + (100/316.23 * 0) + (200/316.23 * 0) = 0.30.

Comparing the dot product result to the example threshold of 0.5 shows that the dot product of RU and CU2 is less than the threshold of 0.5 and close to 0. As described above, such a result indicates that the audio signal 126 is not emanating from the media presentation device 120, and, therefore, the media presentation device 120 is inferred to be turned off, turned down, or muted so as to not be detectable by the microphones 132, 134.

In the illustrated example, the weight adjuster 304 generates a new set of baseline filter coefficients W_(m1) periodically and/or occasionally (e.g., every thirty seconds, every thirty minutes, upon receiving feedback from the decoder 138, creditor 139, and/or AME 160 for bad or otherwise inaccurate result, etc.). For example, the weight adjuster 304 can generate a new reference vector of filter coefficients periodically, in response to a certain number or time period of “off” determinations, in response to a confirmed watermark extraction, etc. For example, the weight adjuster 304 can periodically recalibrate by calculating the reference vector of filter coefficients when a watermark analysis confirms that the media presentation device 120 is turned “on” and emitting valid audio data. The baseline or reference coefficients W_(m1) may be stored for use by the adaptive audio filter 302, the audio comparator 306, and the state determiner 308 in subsequent audio signal analysis and dot product computation, for example.

FIG. 7 shows an example implementation of the state determiner 308 shown and described above with respect to the example of FIG. 3. As shown in the example of FIG. 7, the example state determiner 308 includes a comparison vector 702, a reference vector 704, a coefficient comparator 706, and a state machine 708 to receive filter weight coefficients from the audio comparator 306, determine a status or operating state of the monitored media presentation device 120, and output the determined device state to the decoder 138 and/or creditor 139, as described above with respect to FIGS. 1-3.

As described above, after the inputs from microphones 132 and 134 have been compared to reconcile the audio and generate the set of filter coefficients, the example audio comparator 306 provides a comparison set of filter coefficients to the example state determiner 308. The set of coefficients forms the comparison vector 702 (e.g., converted to a unit vector as described above). The state determiner 308 receives a baseline or reference set of vector coefficients (e.g., from a known or confirmed “on” state of the media presentation device) from the weight adjuster 304 and/or otherwise stores reference coefficients as the reference vector 704 (e.g., converted to a unit vector as described above). The coefficient comparator 706 compares the comparison vector 702 to the reference vector 704 to determine if the filter weight characteristics of the currently captured audio are similar to the reference characteristics of the “known” media presentation device 120 audio. For example, a dot product of the comparison vector 702 and the reference vector 704 yields a value indicative of the similarity or dissimilarity between the comparison vector 702 and the reference vector 704 (and, thereby, the current audio signal 126 and the previously evaluated reference audio signal).

Based on the similarity value determined by the coefficient comparator 706, the state machine 708 infers and/or otherwise determines a state or status of the monitored media presentation device 120. For example, if the similarity value indicates that the comparison vector 702 and the reference vector 704 are identical or similar (e.g., a dot product of the vectors 702, 704 is greater than a threshold (0.5, for example), such as near 1.0), then the state machine 708 indicates or infers that the monitored media presentation device 120 is turned on and is the source of the detected audio signal 126. However, if the similarity value indicates that the comparison vector 702 and the reference vector 704 are not similar (e.g., a dot product of the vectors 702, 704 is less than the threshold, such as near 0), then the state machine 708 indicates or infers that the monitored media presentation device 120 is turned off or is otherwise not outputting detectable audio (e.g., is muted, the volume is turned down past a detectable threshold, etc.). Thus, a source of the audio detected by the microphones 132, 134 is other than the media presentation device 120. The state of the media presentation device 120 provided by the state machine 708 (e.g., on, off, etc.) is sent to the decoder 138 and/or creditor 139 to further process or not process the detected audio (e.g., to process the audio signal 126 from the media presentation device 120 to extract a watermark, calculate a signature, and/or otherwise determine media exposure data, for example).

While an example manner of implementing the source detector 136 and filter apparatus 600 are illustrated in FIGS. 1-3 and 6-7, one or more of the elements, processes and/or devices illustrated in FIGS. 1-3 and 6-7 may be combined, divided, re-arranged, omitted, eliminated and/or implemented in any other way. Further, the example adaptive audio filter 302, the example weight adjuster 304, the example audio comparator 306, the example state determiner 308, and/or, more generally, the example source detector 136 and/or example filter apparatus 600 of FIGS. 1, 2, 3, and 6-7 may be implemented by hardware, software, firmware and/or any combination of hardware, software and/or firmware. Thus, for example, any of the example adaptive audio filter 302, the example weight adjuster 304, the example audio comparator 306, the example state determiner 308, and/or, more generally, the example source detector 136 and/or the filter apparatus 600 can be implemented by one or more analog or digital circuit(s), logic circuits, programmable processor(s), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)). When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the example adaptive audio filter 302, the example weight adjuster 304, the example audio comparator 306, the example state determiner 308, and the example filer apparatus 600 is/are hereby expressly defined to include a tangible computer readable storage device or storage disk such as a memory, a digital versatile disk (DVD), a compact disk (CD), a Blu-ray disk, etc. storing the software and/or firmware. Further still, the example source detector 136 and filter apparatus 600 of FIGS. 1, 2, 3, 6, and 7 may include one or more elements, processes and/or devices in addition to, or instead of, those illustrated in FIGS. 1-3 and 6-7, and/or may include more than one of any or all of the illustrated elements, processes and devices.

Example Monitoring and Determination Methods

Flowcharts representative of example machine readable instructions for implementing the example source detector 136 and filter apparatus 600 of FIGS. 1-3 and 6-7 are shown in FIGS. 8-10. In this example, the machine readable instructions comprise a program for execution by a processor such as the processor 1112 shown in the example processor platform 1100 discussed below in connection with FIG. 11. The program may be embodied in software stored on a tangible computer readable storage medium such as a CD-ROM, a floppy disk, a hard drive, a digital versatile disk (DVD), a Blu-ray disk, or a memory associated with the processor 1112, but the entire program and/or parts thereof could alternatively be executed by a device other than the processor 1112 and/or embodied in firmware or dedicated hardware. Further, although the example program is described with reference to the flowcharts illustrated in FIGS. 8-10, many other methods of implementing the example source detector 136 and filter apparatus 600 of FIGS. 1-3 and 6-7 may alternatively be used. For example, the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, or combined.

As mentioned above, the example processes of FIGS. 8-10 may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a tangible computer readable storage medium such as a hard disk drive, a flash memory, a read-only memory (ROM), a compact disk (CD), a digital versatile disk (DVD), a cache, a random-access memory (RAM) and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term tangible computer readable storage medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, “tangible computer readable storage medium” and “tangible machine readable storage medium” are used interchangeably. Additionally or alternatively, the example processes of FIGS. 8-10 may be implemented using coded instructions (e.g., computer and/or machine readable instructions) stored on a non-transitory computer and/or machine readable medium such as a hard disk drive, a flash memory, a read-only memory, a compact disk, a digital versatile disk, a cache, a random-access memory and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the term non-transitory computer readable medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. As used herein, when the phrase “at least” is used as the transition term in a preamble of a claim, it is open-ended in the same manner as the term “comprising” is open ended.

FIG. 8 is a flow diagram representative of example machine readable instructions 800 that may be executed to implement a monitoring and audience measurement process including the example metering device 130 of FIG. 1 and its components (see, e.g., FIGS. 1, 2, 3, and 6-7). At block 802, a reference vector of filter coefficients is determined as part of a calibration of the source detector 136 for audio monitoring in the room 110. For example, the echo cancellation algorithm of Equations 1-3 and the adaptive filter apparatus 600 are applied by the example adaptive audio filter 302 (FIG. 3) to known audio captured from each of the plurality of microphones 132, 134. As disclosed above with respect to FIGS. 1-7, a baseline or reference vector (e.g., such as the reference vector 704 of the example of FIG. 7) of filter coefficients is generated by the source detector 136 (e.g., the example weight adjuster 304 of the example of FIG. 3) for use in determining an identity and/or location of an audio source (e.g., the media presentation device 120, audience member 140, and/or audience member 142).

At block 804, the example metering device 130 (FIG. 1) monitors the room 110 to detect and capture audio via multiple microphones 132 and 134. For example, microphones 132, 134 in the example meter 130 operate to capture audio 126, 144, and/or 146 audible within range of the microphones 132, 134 in the room 110.

In some examples, before advancing to block 806, captured audio is analyzed to identify a watermark in the captured audio signal. If a watermark is found, then, the watermark information can be used to identify media content associated with the audio (e.g., at block 814 below). In some examples, a reliability score associated with the watermark can also be evaluated to determine whether the watermark is reliable enough for use in media identification. For example, if a watermark is detected from audio emanating from another device in an adjacent room (e.g., a device other than the monitored media presentation device 120), then the distance (and its associated noise affect) from the metering device 130 and its microphones 132, 134 can result in an inadvertently detected watermark with a low reliability score.

Alternatively or in addition to the reliability score, a volume level of the captured audio signal can be analyzed to determine whether the watermark has been detected in an audio signal near the metering device 130 or far from the metering device 130 (e.g., is originating from the monitored media presentation device 120 near the metering device 130 or is originating from another device away from the metering device 130).

In such examples, upon determination of a low score, low volume, etc., associated with a detected watermark, further analysis of the audio signal can then proceed to block 806 as described below. Additionally, if no watermark is identified in the captured audio, then analysis moves to block 806 below.

At block 806, the example source detector 136 (FIG. 1) (and its adaptive audio filter 302, weight adjuster 304, and audio comparator 306 (FIG. 3)) processes the captured audio signal to generate a comparison vector (e.g., such as the comparison vector 702 of the example of FIG. 7). For example, the echo cancellation algorithm of Equations 1-3 and the adaptive filter apparatus 600 are applied to the audio captured from each of the plurality of microphones 132, 134. As disclosed above with respect to FIGS. 1-7, a vector of filter coefficients is generated by the source detector 136 for comparison against the reference vector to determine whether or not the captured audio is generated by the media presentation device 120 and/or by another ambient source such as the audience members 140, 142.

At block 808, the example source detector 136 (FIG. 1) (and its audio comparator 306 (FIG. 3)) compares the comparison vector for the captured audio signal to the reference vector to generate a similarity value. For example, a dot product is computed between the comparison vector coefficients and the reference vector coefficients to determine a similarity or difference between the vectors. Such a similarity or difference in the audio filter coefficients is indicative of a location of origin for the audio signal, allowing the example source detector 136 to determine whether a likely source for the audio signal 126 is or is not the media presentation device 120, for example.

If the captured audio is determined to be emanating from the “known” location of the media presentation device 120, then the dot product comparison yields a value of approximately 1.0, indicating a similarity between the vectors. At block 810, such a result processed by the example state determiner 308 indicates that the media presentation device 120 is turned “on” and the audio matches the characteristics of sound coming from the media presentation device 120 (e.g., audio 126 from the television).

If the captured audio is determined to be ambient audio (e.g., emanating from an audience member 140, 142 and/or other unidentified source such as a device in an adjacent room, etc.), then the dot product comparison yields a value of well below 0.5, indicating that the vectors are dissimilar. At block 812, such a result processed by the example state determiner 308 indicates that the media presentation device 120 is turned “off” (or has been muted or has the volume set too low to be detectable by the microphones, etc.). In some examples, if the media presentation device 120 is determined to be “off”, then the creditor 139 of the example metering device 130 discards, ignores, and/or marks as invalid the captured audio signal and associated information (e.g., timestamp, erroneous code, etc.).

At block 814, if the media presentation device 120 is determined to be on, then the example metering device 130 analyzes the captured audio. For example, the metering device 130 extracts a watermark from the captured audio signal. Alternatively or in addition, the example metering device 130 can process the audio signal to determine a signature for further analysis, for example. For example, the example decoder 138 decodes the captured audio signal to identify a watermark embedded in the audio signal and/or process the captured audio signal to compute a signature associated with the signal in the absence of a watermark. Identification of the watermark and processing of a signature from the captured audio signal may occur in conjunction with the AME 160 as well as with the decoder 138 and creditor 139 of the example meter 130, for example.

At block 816, media exposure information is logged based on the signal analysis (e.g., based on the identified watermark and/or computed signature information). For example, based on the identification of the extracted watermark, the example creditor 139 captures an identification of the media exposure based on the decoded watermark. The creditor 139 may also assign a location identifier, timestamp, etc., to the decoded data. The creditor 139 may transmit and/or otherwise work in conjunction with the AME 160 via the network 150, for example.

At block 818, results of the comparison of vectors at block 708 are evaluated to determine whether reference vector coefficients should be recalibrated. For example, changed conditions in the room 110 (e.g., additional audience members 140, 142, moved furniture, repositioning of the media presentation device 120, etc.) can affect the coefficients indicating the location of the media presentation device 120 and the distinction between the media presentation device 120 and other ambient audio sources (e.g., audience member 140, 142, etc.). In some examples, the example state determiner 308 may determine whether or not to trigger a recalibration of the reference vector based on the available information.

Alternatively or in addition to evaluating the vector comparison, recalibration of the reference coefficients can be triggered based on confirmation of a valid watermark in the captured audio signal. For example, as described above, identification of a watermark in a captured audio signal and computation of a score associated with the watermark to determine its reliability can validate that the media presentation device 120 is turned on and is outputting an audio signal 126 indicative of media content exposed to the room 110. Thus, the operating state of the monitored media presentation device 120 and the validity of its audio output can be automatically determined and used to periodically verify or recalculate the reference vector of filter weight coefficients. Such automated recalibration can be conducted continuously, after passage of a certain period of time, triggered based on a consecutive number of dissimilar results, etc.

At block 820, if recalibration is triggered (e.g., based on the results of the comparison, based on an accurate extraction and identification of watermark data, triggered upon request, etc.), then weighted filter coefficients for the reference vector are re-calculated using an adaptive echo cancellation algorithm such as the filter algorithm of Equations 1-3 and the adaptive filter apparatus 600 of FIG. 6, which is applied to an updated known audio sample (e.g., program audio generated when the media presentation device 120 is known to be turned on) captured from each of the plurality of microphones 132, 134.

At block 822, state information is evaluated by the state determiner 308 to determine whether monitoring is to continue. For example, state information for the metering device 130 and/or instructions from the AME 160 are evaluated by the example state determiner 308 to determine whether to continue monitoring for audio from the media presentation device 120 in the room 110. If the example state determiner 308 determines that monitoring is to continue, then control returns to block 804 to monitor for a new audio signal. Otherwise, if the example state determiner 308 determines that monitoring is not to continue, then the example process 800 ends.

FIG. 9 is a flow diagram representative of example machine readable instructions that may be executed to implement the example filter apparatus 600 of FIG. 6 and block 802 of the example process 800 of FIG. 8 to process incoming audio to calculate filter taps or coefficients for comparison to determine a state of the media presentation device 120 (FIG. 1). While the example process of FIG. 9 as shown provides additional detail regarding execution of block 802 of the example process 800 of FIG. 8 to provide a reference vector, the example process of FIG. 9 can also be applied to generate a comparison vector (block 806) of comparison filter weight coefficients and/or to recalibrate reference vector coefficients (block 820) for audio signal analysis, for example.

At block 902, audio samples are received. For example, audio samples 602 are received by the example microphone 132. At block 904, the received audio samples are processed. For example, audio samples 602 received by the microphone 132 are passed through a delay line 604 such that M samples are shifted by a delay D. In the illustrated example, X_(M−1) is a most recent sample, and X₀ is an oldest sample. An output Y₀ is summed from samples as weighted by a reference set of coefficients {W_(m), m=0,1, . . . M−1} using Equation 1 applied to the filter apparatus 600.

At block 906, the processed audio samples from the first microphone are compared to audio samples acquired from a second microphone. For example, the output Y₀ is subtracted from audio sample(s) X_(d) 606 received by the example microphone 134. Thus, if the summed total of the weighted audio samples X_(M−1) to X₀ (as shifted using shift registers D) approximately matches the audio sample Xd, a difference between X_(d) and Y₀ is approximately zero.

At block 908, the difference between X_(d) and Y₀ is evaluated to determine whether the difference is approximately zero or is significantly greater than zero. At block 910, if the difference is approximately zero, then weights in the reference vector may remain unchanged. If, however, the difference is greater than a threshold above zero, then, at block 912, weights in the reference vector (e.g., W_(M−1), W_(M−2), W_(M), . . . , W₀) are adjusted to new values based on Equations 2 and 3 disclosed above. For example, movement of the media presentation device 120, presence of audience members 140, 142, presence of furniture, etc., in the room 110 may result in a change in sound characteristics that affects the weights in the reference vector and trigger adjustment of reference vector weights.

At block 914, the reference vector is made available for use. For example, if weights were adjusted at block 912, the updated reference vector is made available for use in determining the state (e.g., identity, on/off status, location, etc.) of the media presentation device 120 in the monitored room 110.

FIG. 10 is a flow diagram representative of example machine readable instructions that may be executed to implement the example source detector 136 of FIGS. 1-3 and its components (e.g., the adaptive audio filter of FIG. 6 and the state determiner of FIG. 7) to determine a state of the media presentation device 120 (FIG. 1). The example process of FIG. 10 provides additional and/or related detail regarding execution of block 808 of the example process 800 of FIG. 8.

Initially, at block 1002, a baseline set of weighted coefficients W_(m1) is received. For example, a reference vector, such as example reference vector 704, is received from the example weight adjuster 304 (FIG. 3), which generates the vector based on audio received by the first and second microphones 132, 134 (FIGS. 1-3) at a first time (e.g., using Equations 1-3 as disclosed above in connection with FIG. 6). At block 1004, a current set of weighted coefficients W_(m2) is received. For example, a comparison vector, such as the example comparison vector 702, is received from the weight adjuster 304, which generates the vector based on audio received by the first and second microphones 132, 134, at a second time after the first time.

At block 1006, the example audio comparator 306 calculates a dot product between W_(m1) and W_(m2). For example, as described above with respect to Equation 4 and FIG. 3, vectors W_(m1) and W_(m2) are converted to unit vectors and analyzed according to a dot product and/or other mathematical calculation. At block 1008, the example state determiner 308 determines if the result of the dot product satisfies (e.g., is greater than) a threshold.

If the result of the dot product satisfies the threshold (e.g., is close to 1.0), then, at block 1010, the media presentation device 120 is determined to be “ON”. That is, based on the result of the dot product, the example state determiner 308 determines that the media presentation device 120 is ON. Based on the determination that the media presentation device 120 is ON, program control continues to block 810.

Otherwise, if the result of the dot product does not satisfy the threshold (e.g., is close to zero), at block 1012, the media presentation device 120 is determined to be “OFF”. That is, based on the result of the dot product, the example state determiner 308 determines that the media presentation device 120 is OFF. Based on the determination that the media presentation device 120 is OFF (or is otherwise not generating detectable audio), program control continues to block 812.

FIG. 11 is a block diagram of an example processor platform 1100 capable of executing the instructions of FIGS. 8-10 to implement the example source detector 136 (and its components) of FIGS. 1-3 and 6-7. The processor platform 1100 can be, for example, a server, a personal computer, a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), a personal digital assistant (PDA), an Internet appliance, a DVD player, a CD player, a digital video recorder, a Blu-ray player, a gaming console, a personal video recorder, a set top box, or any other type of computing device.

The processor platform 1100 of the illustrated example includes a processor 1112. The processor 1112 of the illustrated example is hardware. For example, the processor 1112 can be implemented by one or more integrated circuits, logic circuits, microprocessors or controllers from any desired family or manufacturer. In the illustrated example, the processor 1112 is structures to include the example adaptive audio filter 302, the example weight adjuster 304, the example audio comparator 306, and the example state determiner 308 of the example source detector 136.

The processor 1112 of the illustrated example includes a local memory 1113 (e.g., a cache). The processor 1112 of the illustrated example is in communication with a main memory including a volatile memory 1114 and a non-volatile memory 1116 via a bus 1118. The volatile memory 1114 may be implemented by Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAMBUS Dynamic Random Access Memory (RDRAM) and/or any other type of random access memory device. The non-volatile memory 1116 may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory 1114, 1116 is controlled by a memory controller.

The processor platform 1100 of the illustrated example also includes an interface circuit 1120. The interface circuit 1120 may be implemented by any type of interface standard, such as an Ethernet interface, a universal serial bus (USB), and/or a PCI express interface.

In the illustrated example, one or more input devices 1122 are connected to the interface circuit 1120. The input device(s) 1122 permit(s) a user to enter data and commands into the processor 1112. The input device(s) can be implemented by, for example, an audio sensor, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, isopoint and/or a voice recognition system.

One or more output devices 1124 are also connected to the interface circuit 1120 of the illustrated example. The output devices 1124 can be implemented, for example, by display devices (e.g., a light emitting diode (LED), an organic light emitting diode (OLED), a liquid crystal display, a cathode ray tube display (CRT), a touchscreen, a tactile output device, a printer and/or speakers). The interface circuit 1120 of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip or a graphics driver processor.

The interface circuit 1120 of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem and/or network interface card to facilitate exchange of data with external machines (e.g., computing devices of any kind) via a network 1126 (e.g., an Ethernet connection, a digital subscriber line (DSL), a telephone line, coaxial cable, a cellular telephone system, etc.).

The processor platform 1100 of the illustrated example also includes one or more mass storage devices 1128 for storing software and/or data. Examples of such mass storage devices 1128 include floppy disk drives, hard drive disks, compact disk drives, Blu-ray disk drives, RAID systems, and digital versatile disk (DVD) drives.

Coded instructions 1132 representing the flow diagrams of FIGS. 8-10 may be stored in the mass storage device 1128, in the volatile memory 1114, in the non-volatile memory 1116, and/or on a removable tangible computer readable storage medium such as a CD or DVD.

From the foregoing, it will be appreciated that examples have been disclosed which allow a meter 130 (FIG. 1) to distinguish between measurable content and ambient sound to determine an operating state of a media presentation device and improve accuracy of audience measurement. Because the meter 130 can automatically and autonomously monitor, analyze, and determine operating state and validity of monitored data, additional devices, panelist involve, and external oversight can be avoided, resulting in increased accuracy and robustness as well as convenience.

Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent. 

What is claimed is:
 1. An apparatus to determine a source of an audio signal captured by a microphone, the apparatus comprising: memory to store instructions; and at least one processor to execute the instructions to at least: calibrate a reference vector of coefficients for audio monitoring using a known audio sample from a location; compare a comparison vector of coefficients for the audio signal captured at the location to the reference vector of coefficients to generate a similarity value; evaluate the similarity value and the comparing of the comparison vector of coefficients to the reference vector of coefficients to determine reliability of the reference vector of coefficients; and when the evaluation determines that the reference vector of coefficients is unreliable, trigger recalibration of the reference vector of coefficients using an updated known audio sample.
 2. The apparatus of claim 1, wherein the coefficients of the reference vector are filter coefficients generated from the known audio sample captured using a plurality of microphones.
 3. The apparatus of claim 1, wherein the coefficients of the reference vector are weighted.
 4. The apparatus of claim 1, wherein the coefficients of the comparison vector are filter coefficients generated from the captured audio signal captured using a plurality of microphones.
 5. The apparatus of claim 4, wherein the coefficients of the reference vector are weighted.
 6. The apparatus of claim 1, wherein the comparing of the comparison vector of coefficients and the reference vector of coefficients includes computing a dot product between the comparison vector of coefficients and the reference vector of coefficients to generate the similarity value.
 7. The apparatus of claim 1, wherein the comparison vector of coefficients is generated from the captured audio signal using echo cancellation and an adaptive filter.
 8. The apparatus of claim 1, wherein recalibration of the reference vector of coefficients is to be triggered by identification of a watermark in the captured audio signal.
 9. The apparatus of claim 1, wherein the reference vector of coefficients is determined to be unreliable based on at least one of a period of time or a number of dissimilar results indicated by the similarity value below a threshold.
 10. A non-transitory computer readable storage medium comprising instructions that, when executed, cause at least one processor to at least: calibrate a reference vector of coefficients for audio monitoring using a known audio sample from a location; compare a comparison vector of coefficients for an audio signal captured at the location to the reference vector of coefficients to generate a similarity value; evaluate the similarity value and the comparing of the comparison vector of coefficients to the reference vector of coefficients to determine reliability of the reference vector of coefficients; and when the evaluation determines that the reference vector of coefficients is unreliable, trigger recalibration of the reference vector of coefficients using an updated known audio sample.
 11. The non-transitory computer readable storage medium of claim 10, wherein the instructions, when executed, cause the at least one processor to generate the coefficients of the reference vector as filter coefficients from the known audio sample captured using a plurality of microphones.
 12. The non-transitory computer readable storage medium of claim 10, wherein the instructions, when executed, cause the at least one processor to weight the coefficients of the reference vector.
 13. The non-transitory computer readable storage medium of claim 10, wherein the instructions, when executed, cause the at least one processor to generate the coefficients of the comparison vector as filter coefficients from the audio signal captured at the location using a plurality of microphones.
 14. The non-transitory computer readable storage medium of claim 13, wherein the instructions, when executed, cause the at least one processor to weight the coefficients of the reference vector.
 15. The non-transitory computer readable storage medium of claim 10, wherein the instructions, when executed, cause the at least one processor to compare the comparison vector of coefficients and the reference vector of coefficients by computing a dot product between the comparison vector of coefficients and the reference vector of coefficients to generate the similarity value.
 16. The non-transitory computer readable storage medium of claim 10, wherein the instructions, when executed, cause the at least one processor to generate the comparison vector of coefficients from the captured audio signal using echo cancellation and an adaptive filter.
 17. The non-transitory computer readable storage medium of claim 10, wherein the instructions, when executed, cause the at least one processor to trigger recalibration of the reference vector of coefficients by identification of a watermark in the captured audio signal.
 18. The non-transitory computer readable storage medium of claim 10, wherein the instructions, when executed, cause the at least one processor to determine that the reference vector of coefficients is unreliable based on at least one of a period of time or a number of dissimilar results indicated by the similarity value below a threshold.
 19. A method to determine a source of an audio signal captured by a microphone, the method comprising: calibrating a reference vector of coefficients for audio monitoring using a known audio sample from a location; comparing a comparison vector of coefficients for an audio signal captured at the location to the reference vector of coefficients to generate a similarity value; evaluating the similarity value and the comparing of the comparison vector of coefficients to the reference vector of coefficients to determine reliability of the reference vector of coefficients; and when the evaluation determines that the reference vector of coefficients is unreliable, triggering recalibration of the reference vector of coefficients using an updated known audio sample.
 20. The method of claim 19, wherein comparing the comparison vector of coefficients and the reference vector of coefficients includes computing a dot product between the comparison vector of coefficients and the reference vector of coefficients to generate the similarity value.
 21. The method of claim 19 wherein triggering recalibration of the reference vector of coefficients includes triggering by identification of a watermark in the captured audio signal.
 22. The method of claim 19, further including generating the comparison vector of coefficients from the captured audio signal using echo cancellation and an adaptive filter. 